Power control and/or modulation feedback techniques in a radio frequency (RF) power amplifier may be implemented with a variety of circuits. These power control and/or modulation feedback circuits include peak detector/sample-and-hold circuits and complex analog circuit loop systems. Many variants of power control and/or modulation feedback techniques have evolved with respect to polar transmitters. In particular, polar transmitters may utilize open loop or closed loop techniques. Open loop implementation may utilize a single control element to control power and amplitude modulation (AM). The open loop systems control the average power during modulation transmission and comprise a sample-and-hold circuit to hold the direct current (DC) power amplifier control voltage while the AM control signal is being introduced. Closed loop polar transmitters continuously monitor and correct modulation quality and forward transmitted power. In general, closed loop implementations include inherently complex analog circuitry. In closed loop systems, the output may be coupled and mixed down to an intermediate frequency (IF). Errors may be corrected using separate amplitude and phase correction loops. Certain conditions, such as imperfect limiting, however, may cause contention for the phase and amplitude correction loops.
Power control and/or modulation feedback techniques in a RF power amplifier also may be implemented with a variety of circuits specifically adapted to the modulation techniques employed. For example, the circuit architecture may be adapted to operate in a polar modulation configuration or may be adapted to operate in a Cartesian modulation configuration, such as, for example, in-phase/quadrature (IQ) modulation configuration. In a polar modulation configuration an input waveform is separated into an amplitude modulation (AM) component and a phase modulation (PM) component. A circuit may be adapted to separate the AM component out of the input waveform and amplify the remaining PM signal. The AM component then may be re-inserted after an amplification stage to restore the modulation back to its original form. In contrast, in a Cartesian (e.g., IQ) architecture modulation configuration, the input waveform is separated into an in-phase (I) component and a quadrature (Q) component. In various implementations, IQ modulation provides an efficient way to transfer information, and it also works well with digital formats. An IQ modulator may be employed to create AM, PM, and frequency modulation (FM) signals or components. It may be desirable to incorporate various modulation architectures in a single transmitter device wherein the particular desired modulation transmitter architecture configuration may be selectable based on various criteria.